linux-kernel - [PATCH 2/3] ipc/sem.c: handle spurious wakeups

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Date:	Sat, 24 Sep 2011 19:37:11 +0200
From:	Manfred Spraul <manfred@...orfullife.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Mike Galbraith <efault@....de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Manfred Spraul <manfred@...orfullife.com>
Subject: [PATCH 2/3] ipc/sem.c: handle spurious wakeups

semtimedop() does not handle spurious wakeups, it returns -EINTR to user space.
Most other schedule() users would just loop and not return to user space.
The patch adds such a loop to semtimedop()

Reported-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Signed-off-by: Manfred Spraul <manfred@...orfullife.com>
---
 ipc/sem.c |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/ipc/sem.c b/ipc/sem.c
index fb13be1..227948f 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -1426,6 +1426,8 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
 
 	queue.status = -EINTR;
 	queue.sleeper = current;
+
+sleep_again:
 	current->state = TASK_INTERRUPTIBLE;
 	sem_unlock(sma);
 
@@ -1478,6 +1480,13 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
 	 */
 	if (timeout && jiffies_left == 0)
 		error = -EAGAIN;
+
+	/*
+	 * If the wakeup was spurious, just retry
+	 */
+	if (error == -EINTR && !signal_pending(current))
+		goto sleep_again;
+
 	unlink_queue(sma, &queue);
 
 out_unlock_free:
-- 
1.7.6

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